The present invention relates generally to an electromagnetic torque motor having a torsionally suspended flapper that is caused to move or deflect slightly in response to electrical signals supplied to electromagnetic torquing coils of the motor. More particularly, the present invention relates to immersible torque motors of the type used, for example, in fuel controls for gas turbines and the like.
The use of electromagnetic torque motors for controlling hydraulic pressure or flow is well known. It is also common to immerse such torque motors in a fluid to damp flapper motions produced by motor torquing. For example, fuel controls for gas turbine engines have torque motors immersed in fuel which is utilized as the hydraulic medium for operating various components elsewhere in the fuel control.
Even though the fuel serving as a hydraulic medium is highly filtered, ferromagnetic particles such as magnetic oxides suspended in the fuel may be present. Over a long period of time the particles accumulate as contaminants in magnetic gaps of the torque motor where a strong magnetic flux field exists. The magnetic gaps are small, in the order of 0.015 inch (0.38mm), and the accumulation of contamination in these gaps eliminates all freedom of motion of the motor armature and connected flapper so that the motor becomes jammed and unresponsive to electrical signals transmitted to it. Engine failure due to the accumulation of contaminants in the torque motor obviously is unacceptable and, therefore, the protection of the torque motors against contaminants suspended in the fuel is desirable.
It is, accordingly, a general object of the present invention to provide a method and apparatus for protecting a torque motor having a movable flapper against contaminants.